elegates to the AFL-CIO biennial convention demanded today that the Reagan administration end its "demeaning vendetta" against the Professional Air Traffic Controllers Organization, but stopped short of calling for a nationwide show of support for the fired controllers.

Delegates waited until the last day of the federation's four-day gathering to deal with the PATCO situation, which has been the subject of much discussion and several proposed resolutions of support.

Labor support for the union, which has been decertified by the Federal Labor Relations Authority, has been complicated by criticism that PATCO had taken on too much in its strike against the government, had failed to seek the advice or support of other unions and, as a result, had brought organized labor a major defeat. Criticism also revolved around PATCO's break with most of organized labor last year when the controllers group endorsed Republican Ronald Reagan in the presidential race.

But PATCO President Robert E. Poli, who addressed the convention today, was received warmly, and he took the occasion to apologize to fellow union leaders for failing to consult with them before pulling his union out on strike Aug. 3.

"We were a small union, a very young union," he told delegates to the AFL-CIO's 14th constitutional convention, which ended here today.

Poli used the past tense to describe PATCO, 11,438 of whose members have been fired. But, perhaps expressing faith that the decertification ruling will be overturned in pending appeals, Poli added: "We will learn from our mistakes, and we will continue."

Criticism of Poli paled in comparison to the repeated attacks on the way Reagan handled the strike. There is a feeling, expressed in numerous conversations and several speeches from the convention floor, that the administration is using PATCO as an example in a national campaign to get tough with unions.

Poli's allegations today supported that thinking. He said five of his union's leaders probably will be convicted of illegally striking against the government--a felony that can result in a one-year prison term--even though the Federal Aviation Administration, the controllers' employing agency, last August said that the strike was over because the strikers had been fired.

The federal government has confiscated cars from 25 PATCO leaders in Indianopolis who face federal charges, "and has made them post a $1,000 bond and charged them $40 a month for storage of their automobiles just for picketing," Poli said. PATCO members elsewhere "have been blacklisted" by private and public employers "who have been advised that they aren't to hire air traffic controllers who struck," Poli said.